Aerogel

ABSTRACT

The present invention pertains to an aerogel having a thermal conductivity of 0.03 W/m·K or less and a compressive elasticity modulus of 2 MPa or less at 25° C. under atmospheric pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 16/141,155 filed inthe U.S. on Sep. 25, 2018, which is a divisional of U.S. Ser. No.15/121,668, filed in the U.S. on Aug. 25, 2016, which is a nationalphase application filed under 35 U.S.C. § 371 of InternationalApplication No. PCT/JP2015/055371, filed on Feb. 25, 2015, which claimspriority from Japanese Patent Application No. 2015-013371, filed Jan.27, 2015, and Japanese Patent Application No. 2014-035155, filed Feb.26, 2014, the entire content of each of which are hereby incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to an aerogel having excellent thermalinsulation and productivity.

BACKGROUND ART

Silica aerogel is known as a material having small thermal conductivityand thermal insulation. Silica aerogel is useful as a functionalmaterial having excellent functionalities (e.g., thermal insulation),unique optical properties, and unique electric properties and is, forexample, used among others as an electronic substrate material thatutilizes the super-low permittivity characteristics of the silicaaerogel, as a thermal insulation material that utilizes the high thermalinsulating property of the silica aerogel, or as a light reflectingmaterial that utilizes the super-low reflective index of the silicaaerogel.

As a process for producing such silica aerogel, there is known asupercritical drying method by which alkoxysilane is hydrolyzed andpolymerized, and the obtained gel compound (alcogel) is dried under thesupercritical conditions of a dispersion medium: for example, PatentLiterature 1 should be referred to. The supercritical drying method is amethod for removing a solvent contained in the alcogel which comprisesintroducing the alcogel and the dispersion medium (the solvent for usein drying) into a pressurized container and applying to the dispersionmedium, a temperature and pressure above its critical point to generatea supercritical fluid. However, since the supercritical drying methodrequires a high pressure process, capital investments in special devicesand others that can endure the supercriticality are necessary, and alsosimultaneously, much time and effort are needed.

Therefore, a technique has been proposed that an alcogel is dried byemploying a commonly used method which does not require the highpressure process. As such method, there is, for example, known a methodby which monoalkyltrialkoxysilane and tetraalkoxysilane as raw gelmaterials are combined at a specific ratio to improve the strength ofthe gel to be obtained and it is dried under normal pressure: forexample, Patent Literature 2 should be referred to. However, when suchnormal pressure drying is employed, the gel tends to shrink because ofthe stress resulting from the capillarity within the alcogel.

CITATION LIST Patent Literature

Patent Literature 1: U.S. Pat. No. 4,402,927B

Patent Literature 2: Japanese Unexamined Patent Publication No.2011-93744

SUMMARY OF INVENTION Technical Problem

While the problems that have been inherent in the conventionalproduction processes are thus examined from different viewpoints, theirproductivities remain to be problems to be solved because even if eitherof the above-described processes is employed, the obtained aerogels arepoor in handling and the scale-up of the processes will be difficult.For example, there are cases where the aerogels in agglomerated formobtained by the above-described processes are damaged simply when theyare touched with hands to be lifted up. This is inferred to arise fromthat the densities of the aerogels are low and the aerogels have porestructures which comprise only fine particles on the order of 10 nmbeing weekly linked.

The technique for improving such problems that the conventional aerogelshave is thought to be a method by which the pore diameter of the gel isallowed to be large to the level of a micro meter scale and the gel isthus imparted with flexibility. However, there is a problem that thethermal conductivity of the thus-obtained aerogel increases drastically,and the excellent thermal insulation of the aerogel is lost.

The present invention has been made in view of the above-describedcircumstances and has an objective of providing an aerogel havingexcellent thermal insulation and productivity.

Solution to Problem

As a result of having repeated diligent studies in order to accomplishthe above-described objective, the present inventors discovered that anyaerogel having a specific range of thermal conductivity as well ashaving a specific range of compressive elasticity modulus displayedexcellent thermal insulation, while improving the handling, whichenabled the production scale-up and thus could increase theproductivity, leading to the completion of the present invention.

The present invention provides an aerogel having a thermal conductivityof 0.03 W/m·K or less and a compressive elasticity modulus of 2 MPa orless at 25° C. under atmospheric pressure. Specifically, the aerogel ofthe present invention is excellent in thermal insulation andproductivity since it has a specific range of thermal conductivity aswell as a specific range of compressive elasticity modulus as opposed tothe aerogels produced according to the prior art. Thereby, excellentthermal insulation is displayed while the handling of the aerogel isimproved to enable the production scale-up and thus the productivity canbe increased.

The aerogel of the present invention allows its recovery rate fromdeformation to be 90% or more. Such aerogel can possess more excellentflexibility.

The aerogel of the present invention allows its maximum compressivedeformation rate to be 80% or more. Such aerogel can posses moreexcellent flexibility.

The present invention provides an aerogel wherein a ratio Q+T:D of asignal area derived from Q and T to a signal area derived from D is from1:0.01 to 1:0.5 when in a solid ²⁹Si-NMR spectrum as measured by usingDD/MAS method, silicon-containing bonding units of Q, T, and D aredefined as described below, providing that an organic group is amono-valent organic group where an atom bonded to a silicon atom is acarbon atom in what follows,

wherein Q: a silicon-containing bonding unit comprising four oxygenatoms that are bonded to one silicon atom;

T: a silicon-containing bonding unit comprising three oxygen atoms andone hydrogen atom or one mono-valent organic group that are bonded toone silicon atom; and

D: a silicon-containing bonding unit comprising two oxygen atoms and twohydrogen atoms or two mono-valent organic groups that are bonded to onesilicon atom.

The present invention provides an aerogel having a structure representedby general formula (1) described below. Such aerogel is excellent inthermal insulation and productivity. The aerogel may easily becontrolled at a specific range of thermal conductivity as well as at aspecific range of compressive elasticity modulus by introducing thestructure represented by the general formula (1) into its skeleton.

wherein in the formula (1), R₁ and R₂ each independently represents analkyl group or an aryl group and R₃ and R₄ each independently representsan alkylene group.

The present invention provides an aerogel having a ladder type structureprovided with a strut and a bridge, the bridge represented by generalformula (2) described below. Such aerogel has excellent flexibilityresulting from the ladder structure while maintaining the thermalinsulation of its own. The aerogel may easily be controlled at aspecific range of thermal conductivity as well as at a specific range ofcompressive elasticity modulus by introducing the thus-mentionedstructure into its skeleton.

wherein in the formula (2), R₆ and R₇ each independently represents analkyl group or an aryl group and “b” represents an integer of from 1 to50.

Further, as the aerogel having a ladder type structure, there ismentioned that which has a structure represented by general formula (3)described below. This allows more excellent thermal insulation andflexibility to be attained.

wherein in the formula (3), R₅, R₆, R₇, and R₈ each independentlyrepresents an alkyl group or an aryl group; “a” and “c” eachindependently represents an integer of from 1 to 3,000; and “b”represents an integer of from 1 to 50.

The present invention also provides an aerogel from drying a wet gel,the wet gel being formed from a sol comprising at least one memberselected from the group consisting of a polysiloxane compound having areactive group within a molecule thereof and a hydrolyzed product ofsaid polysiloxane compound. The thus-obtained aerogel is excellent inthermal insulation and productivity. In addition, the aerogel may easilybe controlled at a specific range of thermal conductivity as well as ata specific range of compressive elasticity modulus by being obtained assuch.

Further, the aerogel described above may be from drying a wet gel, thewet gel being formed from a sol comprising at least one member selectedfrom the group consisting of a polysiloxane compound having a reactivegroup within a molecule thereof and a hydrolyzed product of saidpolysiloxane compound.

Here, as the reactive group, a hydroxyalkyl group is mentioned, and thecarbon number of said hydroxyalkyl group can be from 1 to 6. This resultin an aerogel having more excellent thermal insulation and flexibility.

In addition, when the reactive group is a hydroxyalkyl group, theabove-described polysiloxane compounds include those represented bygeneral formula (4) described below. This allows more excellent thermalinsulation and flexibility to be attained.

wherein in the formula (4), R₉ represents a hydroxyalkyl group; R₁₀represents an alkylene group; R₁₁ and R₁₂ each independently representsan alkyl group or an aryl group; and “n” represents an integer of from 1to 50.

In the present invention, as the reactive group, an alkoxy group is alsomentioned, and the carbon number of said alkoxy group can be from 1 to6. This results in an aerogel having more excellent thermal insulationand flexibility.

In addition, when the reactive group is an alkoxy group, thepolysiloxane compounds include those represented by general formula (5)described below. This allows more excellent thermal insulation andflexibility to be attained.

wherein in the formula (5), R₁₄ represents an alkyl group or an alkoxygroup; R₁₅ and R₁₆ each independently represents an alkoxy group; R₁₇and R₁₈ each independently represents an alkyl group or an aryl group;and “in” represents an integer of from 1 to 50.

In the present invention, the above-described sol may further compriseat least one member selected from the group consisting of a siliconecompound having a hydrolyzable functional group within a moleculethereof and a hydrolyzed product of said silicone compound. This allowsmore excellent thermal insulation and productivity to be attained.

The above-described drying can also be carried out at a temperature ofless than a critical point of a solvent to be used in the drying andunder atmospheric pressure, which may be supercritical drying. Thereby,an aerogel that is excellent in thermal insulation and productivity canfurther be easily obtained.

Advantageous Effects of Invention

According to the present invention, there can be provided an aerogelthat is excellent in thermal insulation and productivity. Specifically,the aerogel having a specific range of thermal conductivity as well as aspecific range of compressive elasticity modulus displays excellentthermal insulation, while improving the handling, which enables theproduction scale-up and can increase the productivity. There has beenthus far no report on the aerogel having a specific range of thermalconductivity as well as a specific range of compressive elasticitymodulus as defined above; the present invention has a potential where itcan be utilized in a variety of usages.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a chart of measurement obtained when the thermal conductivityof an aerogel of the present embodiment was measured under atmosphericpressure by using a steady state thermal conductivity measuring device.

FIG. 2 is a stress-distortion curve obtained when the aerogel of thepresent invention with a compressive elasticity modulus of 0.20 MPa wasmeasured.

FIG. 3 is a diagram showing a solid ²⁹Si-NMR spectrum of silicasurface-treated with 3-(trimethoxysilyl)propyl methacrylate as measuredusing DD/MAS method.

FIG. 4 is a diagram showing a solid ²⁹Si-NMR spectrum of silicone rubberas measured using the DD/MAS method.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention will be hereinbelowdescribed in detail while referring to the figures where necessary.However, the present invention is not to be limited to the embodimentsas described below.

<Aerogels>

In accordance with the narrow definition against wet gels, the dry gelsobtained using the supercritical drying method are referred to asaerogels; the dry gels obtained using drying under atmospheric pressureare referred to as xerogels; and the dry gels obtained using freezedrying are referred to as cryogels. However, in the present embodiments,the dry gel with a low density obtained regardless of any of thesedrying methods for the wet gel will be referred to as an aerogel.Specifically, the aerogel of the present embodiment is an aerogel in thebroad definition, which implies a gel comprised of a microporous solidin which the dispersed phase is a gas. Generally, the interior of anaerogel comprises a reticulate fine structure and has a clusterstructure where aerogel particles of the order of 2-20 nm are bonded.There are fine pores that are less than 100 nm between the skeletonsformed by this cluster, leading to a fine porous structurethree-dimensionally. Further, the aerogels in the present embodimentsare silica aerogels comprising silica as the principal component. As thesilica aerogel, there is mentioned an aerogel of the so-calledorganic-inorganic hybridized type. The aerogels of the presentembodiments are those which are excellent in thermal insulation andproductivity (flexibility).

[Thermal Conductivity]

The aerogel of the present embodiment has a thermal conductivity of 0.03W/m·K or less at 25° C. under atmospheric pressure. The thermalconductivity even may be 0.025 W/m·K or less and may be 0.02 W/m·K orless. If the thermal conductivity is 0.03 W/m·K or less, it will bepossible to obtain thermal insulation that is greater than that of apolyurethane foam which is a high performance insulating material. Notethat the lower limit of thermal conductivity is not particularlyrestricted, but it can be, for example, set at 0.01 W/m·K.

The thermal conductivity can be measured by the steady state method.Concretely, measurement can be made using a steady state thermalconductivity measuring device “FM436Lambda” (product name; HFM436Lambdabeing a registered trademark: manufactured by NETZSCH GmbH & Co.). FIG.1 is a diagram showing a chart of measurement obtained when the thermalconductivity of the aerogel of Example 10 to be described later wasmeasured under atmospheric pressure by using this steady state thermalconductivity measuring device. According to FIG. 1, it is understoodthat the aerogel of the present example which was actually measured hasa thermal conductivity of 0.020 W/m·K at 25° C.

The outline of the method of measuring thermal conductivity with thesteady state thermal conductivity measuring device is as follows.

(Preparation of Sample for Measurement)

By using a blade with an edge angle of from about 20 to 25 degrees, anaerogel is processed into a size of from 150×150×100 mm³ to make asample for measurement. Note that in HFM436 Lambda the recommendedsample size is 300×300×100 mm³; however, it was already ascertained thatthe thermal conductivity as measured with the sample size proved to beat the same level as the thermal conductivity as measured with therecommended sample size. If necessary, the sample for measurement isnext shaped with sandpaper of #1500 and above to secure the parallelismof the surfaces. Further, prior to the measurement of thermalconductivity, a constant temperature drying oven “DVS402” (product name:manufactured by Yamato Scientific Co. Ltd) is used to dry the sample formeasurement at 100° C. for 30 minutes under atmospheric pressure. Thesample for measurement is then transferred into a desiccator and iscooled to 25° C. This allows the sample for the thermal conductivitymeasurement to be obtained.

(Method of Measurement)

The measurement conditions are at an average temperature of 25° C. andunder atmospheric pressure. The sample for measurement obtained asdescribed above is sandwiched between an upper heater and a lower heaterat a load of 0.3 Pa to set a temperature differential ΔT of 20° C. andis adjusted such that one-dimensional heat flow is formed by a guardheater, while the upper surface temperature and the lower surfacetemperature of the sample for measurement are measured. Then, thermalresistance R_(S) of the sample for measurement is determined accordingto the following equation:

R _(S) =N((T _(U) −T _(L))/Q)−R _(O)

wherein T_(U) represents an upper surface temperature of the sample formeasurement; T_(L) represents a lower surface temperature of the samplefor measurement; R_(O) represents a contact thermal resistance of aninterface between the upper and lower surfaces; and Q represents anoutput of a heat flux meter. Note that N is a proportionalitycoefficient and is determined in advance by using a calibration sample.

Thermal conductivity λ of the sample for measurement is determined fromthe obtained thermal resistance R_(S) according to the followingequation:

λ=d/R _(S)

-   -   wherein “d” represents a thickness of the sample for        measurement.

[Compressive Elasticity Modulus]

The aerogel of the present embodiment has a compressive elasticitymodulus of 2 MPa or less at 25° C. Further, the compressive elasticitymodulus may be 1 MPa or less and may be 0.5 MPa or less. If thecompressive elasticity modulus is 2M Pa or less, the aerogel whosehandling is excellent can result. In addition, the lower limit of thecompressive elasticity modulus is not particularly restricted but can,for example, be 0.05 MPa.

[Recovery Rate from Deformation]

The aerogel of the present embodiment can have a recovery rate fromdeformation to be 90% or more at 25° C. Further, the recovery rate fromdeformation may be 94% or more and may be 98% or more. If the recoveryrate from deformation is 90% or more, it will be easier to obtainexcellent strength, excellent flexibility against deformation, and thelike. In addition, the upper limit of the recovery rate from deformationis not particularly restricted but can, for example, be 100% and even be99%.

[Maximum Compressive Deformation Rate]

The aerogel of the present embodiment can have a maximum compressivedeformation rate to be 80% or more at 25° C. Further, the maximumcompressive deformation rate may be 83% or more and may be 86% or more.If the maximum compressive deformation rate is 80% or more, it will beeasier to obtain excellent strength, excellent flexibility againstdeformation, and the like. In addition, the upper limit of the maximumcompressive deformation rate is not particularly restricted but can, forexample, be 90%.

These compressive elasticity modulus, recovery rate from deformation,and maximum compressive deformation rate can be measured using a smallsize desk top type tester “EZTest” (product name: manufactured byShimadzu Corporation). The outline of the method of measuring thecompressive elasticity modulus and others, which employs the small sizedesk top type tester, is as follows.

(Preparation of Sample for Measurement)

By using a blade with an edge angle of from about 20 to about 25degrees, an aerogel is processed into a cube of 7.0 mm square (in diceform) to make a sample for measurement. If necessary, the sample formeasurement is next shaped with sandpaper of #1500 and above to securethe parallelism of surfaces. Further, prior to the measurement, theconstant temperature drying oven “DVS402” (product name: manufactured byYamato Scientific Co. Ltd.) is used to dry the sample for measurement at100° C. for 30 minutes under atmospheric pressure. The sample formeasurement is then transferred into a desiccator and is cooled to 25°C. Thereby, the samples for measurement of the compressive elasticitymodulus, recovery rate from deformation, and maximum compressivedeformation are obtained.

(Method of Measurement)

A load cell with 500 N is to be used. Also, an upper platen (ϕ 20 mm)and a lower platen (ϕ 118 mm), which are made of stainless steel, areused as compression measurement jigs. The sample for measurement is setbetween the jigs, and compression is carried out at a rate of 1 mm/min,where the deviation in the size of the sample for measurement at 25° C.is measured. The measurement is caused to end at a point that a loadexceeding 500 N is applied or the sample for measurement is destroyed.Here, compressive strain ε can be determined according to the followingequation:

ε=Δd/d1

-   -   wherein Δd represents a deviation (mm) in the thickness of the        sample for measurement under load and d1 represents a        thickness (mm) of the sample for measurement before the load is        applied.

Further, compressive stress σ (MPa) can be determined according to thefollowing equation:

σ=F/A

-   -   wherein F represents compressive force (N) and A represents a        cross section area (mm²) of the sample for measurement before        the load is applied.

FIG. 2 is a diagram showing a curve of compressive stress-compressivestrain of the aerogel of the present Example 1 to be described later.Further, compressive elasticity modulus E (MPa) can be determined, forexample, in the range of compressive force being from 0.1 to 0.2 Naccording to the following equation:

E=(σ₂−σ₁)/(ε₂−ε1)

wherein σ₁ represents compressive stress (MPa) measured when thecompressive force is 0.1 N; σ₂ represents compressive stress (MPa)measured when the compressive force is 0.2 N; ε₁ represents compressivestrain measured when the compressive stress is σ₁; and ε₂ is compressivestrain measured when the compressive stress is σ₂.

According to FIG. 2 and the above equation, it is found that the aerogelof the present Example, which has been actually subjected to themeasurement, has a compressive elasticity modulus of 0.20 MPa at 25° C.

On the other hand, the recovery rate from deformation and the maximumcompressive deformation rate can be calculated according to the equationdescribed below, providing that the thickness of a sample formeasurement before the load is applied is d1, the thickness of thesample for measurement at a point that a maximum load of 500 N isapplied or the sample for measurement is destroyed is d2, and thethickness of the sample for measurement after the load has been removedis d3.

Recovery rate from deformation=(d3−d2)/(d1−d2)×100

Maximum compressive deformation rate=(d1−d2)/d1×100

Moreover, these thermal conductivity, compressive elasticity modulus,recovery rate from deformation, and maximum compressive deformation ratecan be appropriately adjusted by changing the production conditions ofthe aerogel, staring materials and the like.

[Signal Areas Relating to Silicon-Containing Bonding Units Q, T, and T]

The aerogel of the present embodiment can be such that a ratio Q+T:D(signal area ratio) of a signal area derived from Q and T to a signalarea derived from D is from 1:0.01 to 1:0.5 when in a solid ²⁹Si-NMRspectrum as measured by using the DD/MAS method, silicon-containingbonding units of Q, T, and D are defined as described below. Further,the signal area ratio may be set at from 1:0.01 to 1:0.3, at from 1:0.02to 1:0.2, or at from 1:0.03 to 1:0.1. If the signal area ratio is set at1:0.01 or more, more excellent flexibility will tend to be easilyobtained; if it is set at 1:0.5 or less, lower thermal conductivity willtend to be easily obtained.

Note that “oxygen atom” in Q, T, and D as described below is mainly anoxygen atom connecting between two silicon atoms but a case where it isan oxygen atom that is possessed by a hydroxyl group and is bonded to asilicon atom is conceivable. Also, “organic group” is a mono-valentorganic group where the atom that is bonded to the silicon atom is acarbon atom; for example, there is mentioned an organic group having acarbon number of from 1 to 10 that is unsubstituted or substituted. Asthe unsubstituted mono-valent organic group, there are mentionedhydrocarbon groups such as an alkyl group, an alkenyl group, an alkynylgroup, a cycloalkyl group, an aryl group, and an aralkyl group. Further,as the substituted mon-valent organic group, there are mentionedhydrocarbon groups (substituted organic group) of which hydrogen atom issubstituted by a halogen atom, a prescribed functional group, aprescribed functionality-containing organic group, or the like, oralternatively, hydrocarbon groups particularly of which a hydrogen atomin a ring of a cycloalkyl group, an aryl group, an aralkyl group or thelike, is substituted by an alkyl group. Furthermore, the halogen atomsinclude a chlorine atom, a fluorine atom, and the like, which will leadto a halogen atom-containing organic group such as a chloroalkyl groupor a polyfluoroalkyl group. The functional groups include a hydroxylgroup, a mercapto group, a carboxyl group, an epoxy group, an aminogroup, a cyano group, an acryloyloxy group, a methacryloxy group, andthe like; and the functionality-containing organic groups include analkoxy group, an acyl group, an acyloxy group, an alkoxycarbonyl group,a glycidyl group, an epoxy cyclohexyl group, an alkylamino group, adi-alkylamino group, an arylamino group, an N-aminoalkyl substitutedaminoalkyl group, and the like, respectively.

Q: a silicon-containing bonding unit comprising four oxygen atoms thatare bonded to one silicon atom;T: a silicon-containing bonding unit comprising three oxygen atoms andone hydrogen atom or one mono-valent organic group that are bonded toone silicon atom; andD: a silicon-containing bonding unit comprising two oxygen atoms and twohydrogen atoms or two mono-valent organic groups that are bonded to onesilicon atom.

If the signal area ratio of Q+T:D is within this range, the thermalinsulation and the productivity can be enhanced.

The signal area ratio can be confirmed with a solid ²⁹Si-NMR spectrum.In general, measurement techniques for the solid ²⁹Si-NMR spectra arenot particularly limited. For example, CP/MAS method and DD/MAS methodare mentioned, and the present embodiments employ the DD/MAS method fromthe standpoint of quantitativity.

Meanwhile, Roychen Joseph at al. have reported the structural analysisof composites of colloidal silica and methyl polymethacrylate by usingsolid ²⁹Si-NMR in Macromolecules, 1996, 29, pp. 1305-1312. Further,Aramata at al. have reported the interface analysis of silica-siloxanein silicone rubbers by using solid ²⁹Si-NMR in BUNSEKI KAGAKU, 1998, 47,pp. 971-978. In measuring solid ²⁹Si-NMR spectra, these reports can bereferred to as appropriate.

Chemical shifts of the silicon-containing bonding units Q, T, and D in asolid ²⁹Si-NMR spectrum are, respectively, observed in the regions whereQ unit: from −90 to −120 ppm; T unit: from −45 to −80 ppm; and D unit:from 0 to −40 ppm. Therefore, it is possible to separate the signals ofthe silicon-containing bonding units Q, T, and D and to calculate thesignal area derived from each unit. Note that in analyzing the spectra,it is possible to employ the exponential function as the Window functionand at the same time to set the Line Broadening coefficient in the rangeof from 0 to 50 Hz, from the standpoint of improving the analyticalaccuracy.

For example, FIG. 3 is a diagram showing a solid ²⁹Si-NMR spectrum ofsilica surface-treated with 3-(trimethoxysilyl)propyl methacrylate asmeasured using the DD/MAS method. Also, FIG. 4 is a diagram showing asolid ²⁹Si-NMR spectrum of silicon rubber as measured using the DD/MASmethod. As FIGS. 3 and 4 show, the separation of silicon-containingbonding units Q, T, and D is possible based on the solid ²⁹Si-NMRspectra using the DD/MAS method.

Here, the method of calculating the signal area ratios will be describedby utilizing FIGS. 3 and 4. For example, in FIG. 3 the Q unit signalderived from silica is observed in the chemical shift range of from −90to −120 ppm. Also, the T unit signal derived from3-(trimethoxysilyl)propyl methacrylate and its reaction product isobserved in the chemical shift range of from −45 to −80 ppm. Signalareas (integrated values) are obtained by integrating the signals in therespective chemical shift ranges. When the signal area of Q unit is set1, the signal area ratio of Q:T in FIG. 3 will be calculated to be1:0.32. Note that the signal areas are calculated with a generalspectrum analysis software (such as NMR software “TopSpin” produced byBruker Inc.; TopSpin is a registered trademark).

Also, In FIG. 4 the Q unit signal in a silicone rubber loaded with fumedsilica is observed in the chemical shift range of from −90 to −120 ppm.Further, the D unit signal in the silicone rubber loaded with fumedsilica is observed in the chemical shift range of from 0 to −40 ppm. Thesignal areas (integrated values) are obtained by integrating the signalsin the respective chemical shift ranges. When the signal area of the Qunit is set 1, the signal area ratio of Q:D in FIG. 4 will be calculatedto be 1:0.04.

[Density and Porosity]

The aerogel of the present embodiment can have the density at 25° C. tobe from 0.05 to 0.25 g/cm³ and may further have it to be from 0.1 to 0.2g/cm³. If the density is 0.05 g/cm³ or more, more excellent strength andflexibility can be obtained; also if it is 0.25 g/cm³ or less, moreexcellent thermal insulation can be obtained.

The aerogel of the present embodiment can have the porosity at 25° C. tobe from 85 to 95% and may further have it to be from 87 to 93%. If theporosity is 85% or more, more excellent thermal insulation can beobtained; also if it is 95% or less, more excellent strength andflexibility can be obtained.

With respect to the aerogel, the central diameters, densities, andporosities of holes (or pores) that are continuously communicating in athree-dimensional reticulate fashion can be measured by the mercurypenetration method in accordance with DIN66133.

<Concrete Forms of Aerogels>

The aerogels of the present embodiments include first to third forms asdescribed below. By employing the first to the third form, it will bepossible to control the thermal conductivity and the compressiveelasticity modulus of the aerogel within specific ranges. Nevertheless,the employment of each of the first to the third forms does notnecessarily aim at acquiring an aerogel having a specific range ofthermal conductivity as well as a specific range of compressiveelasticity modulus which are defined by the present embodiments. Byemploying each form, an aerogel having a thermal conductivity and acompressive elasticity modulus depending on the each form can beobtained.

(First Form)

The aerogel of the present embodiment can have a structure representedby the following general formula (1):

In the formula (1), R₁ and R₂ each independently represents an alkylgroup or an aryl group, and R₃ and R₄ each independently represents analkylene group. Here, the aryl groups include a phenyl group, asubstituted phenyl group, and others. Further, examples of thesubstituent in the substituted phenyl group include, an alkyl group, avinyl group, a mercapto group, an amino group, a nitro group, and acyano group.

By introducing the above-described structure introduced into theskeleton of an aerogel, the aerogel with low thermal conductivity andflexibility will result. From such standpoint, in the formula (1) as R¹and R², there are respectively, independently mentioned an alkyl grouphaving a carbon number of from 1 to 6, a phenyl group, and the like, andas said alkyl group, there is mentioned a methyl group or the like.Also, in the formula (1) as R³ and R⁴, there are respectively,independently mentioned an alkylene group having a carbon number of from1 to 6 or the like, and as said alkylene group, there is mentioned anethylene group, a propylene group, or the like.

(Second Form)

The aerogel of the present embodiment is an aerogel having a ladder typestructure that is provided with a strut(s) and a bridge(s) and may be anaerogel of which the bridge is represented by general formula (2)described below. By introducing such ladder type structure into theskeleton of an aerogel, thermal resistance and mechanical strength canbe improved. Note that the “ladder type structure” in the presentembodiments is that which has two struts and bridges linking therespective struts (i.e., having a form of “ladder”). Although theaerogel skeleton may be comprised of the ladder type structure in thepresent form, the aerogel may partially have the ladder type structure.

In the formula (2), R₆ and R₇ each independently represents an alkylgroup or an aryl group and “b” represents an integer of from 1 to 50.Here, the aryl groups include a phenyl group, a substituted phenylgroup, and others. Further, examples of the substituent in thesubstituted phenyl group include an alkyl group, a vinyl group, amercapto group, an amino group, a nitro group, and a cyano group.Further, when “b” is an integer of 2 or more in the formula (2), two ormore R₆s may, respectively, be identical or different and two or moreR₇s may, respectively, be identical or different similarly.

By introducing the above-described structure into the skeleton of anaerogel, there will be produced an aerogel having more excellentflexibility than does the aerogel having a structure derived fromsilsesquioxane of the conventional ladder type (i.e., one having astructure represented by general formula (X) described below) as anexample. Note that as is shown by the general formula (X) describedbelow, the structure of the bridge is —O— in the aerogel having astructure derived from silsesquioxane of the conventional ladder typebut that the structure of the bridge is a structure represented by thegeneral formula (2) described above (polysiloxane structure) in theaerogel of the present embodiment.

In the formula (X), R represents a hydroxyl group, an alkyl group, or anaryl group.

The structure to be the strut and its chain length, as well as thedistance between the structures to be the bridges is not particularlylimited; however, as the ladder type structure, there is mentioned astructure represented by general formula (3) described below from thestandpoint of improving thermal resistance and mechanical strength.

In the formula (3), R₅, R₆, R₇, and R₈ each independently represents analkyl group or an aryl group and “a” and “c” each independentlyrepresents an integer of from 1 to 3,000. Here, the aryl groups includea phenyl group, a substituted phenyl group, and others. Further,examples of the substituent in the substituted phenyl group include analkyl group, a vinyl group, a mercapto group, an amino group, a nitrogroup, and a cyano group. Further, when “b” is an integer of 2 or morein the formula (3), two or more R₆s may, respectively, be identical ordifferent and two or more R₇s may, respectively, be identical ordifferent similarly. Still further, when “a” is an integer of 2 or morein the formula (3), two or more R₅s may, respectively, be identical ordifferent and two or more R₅s may, respectively, be identical ordifferent similarly.

In addition, from the standpoint of obtaining more excellentflexibility, there are respectively, independently mentioned an alkylgroup having a carbon atom of from 1 to 6, a phenyl group, and the likeas R₅, R₇, R₇, and R₈ in the formula (2) and formula (3) [providing thatR₅ and R₈ are only in the formula (3)]; and said alkyl groups include amethyl group and the like. Moreover, “a” and “c” in the formula (3) canbe each independently from 6 to 2,000 and may further be from 10 to1,000. Also, “b” in the formula (2) and formula (3) can be from 2 to 30and may further be from 5 to 20.

(Third Form)

The aerogel of the present embodiment may be one obtainable by drying awet gel, the wet gel being formed from a sol comprising at least onemember selected from the group consisting of a polysiloxane compoundhaving a reactive group within a molecule thereof and a hydrolyzedproduct of said polysiloxane compound. Further, the aerogels that havebeen mentioned so far may be those obtainable by drying wet gels, thewet gels being formed from sols comprising at least one member selectedfrom the group consisting of a polysiloxane compound having a reactivegroup within a molecule thereof and a hydrolyzed product of saidpolysiloxane compound.

The reactive group in the polysiloxane compound having a reactive groupis not particularly limited, but its examples include an alkoxy group, asilanol group, a hydroxyalkyl group, an epoxy group, a polyether group,a mercapto group, a carboxyl group, and a phenol group. The polysiloxanecompound having these reactive groups may be used singly or incombination of two or more kinds. Among these, the alkoxy group, silanolgroup, hydroxyalkyl group or the polyether group can improve theflexibility of the aerogel, and furthermore, the alkoxy group or thehydroxyalkyl group can improve the compatibility of sols. Also, from thestandpoint of improving the reactivity of the polysiloxane compound aswell as of decreasing the thermal conductivity of the aerogel, therespective carbon numbers of the alkoxy group and the hydroxyalkyl groupcan be from 1 to 6; they can further be from 2 to 4 from the standpointof more improving the flexibility of the aerogel.

As the polysiloxane compound having a hydroxyalkyl group within amolecule thereof, there is mentioned one having a structure representedby general formula (4) described below. By using the polysiloxanecompound having the general formula (4), the structure represented bythe general formula (1) described previously can be introduced into theskeleton of an aerogel.

In the formula (4), R₉ represents a hydroxyalkyl group; R₁₀ representsan alkylene group; R₁₁ and R₁₂ each independently represents an alkylgroup or an aryl group; and “n” represents an integer of from 1 to 50.Here, the aryl groups include a phenyl group, a substituted phenylgroup, and others. Further, examples of the substituent in thesubstituted phenyl group include an alkyl group, a vinyl group, amercapto group, an amino group, a nitro group, and a cyano group.Further, in the formula (4), two or more R₉s may, respectively, beidentical or different and two or more R₁₀s may, respectively, beidentical or different similarly. Still further, in the formula (4), twoor more R₁₁s may, respectively, be identical or different and two ormore R₁₂s may, respectively, be identical or different similarly.

By using the wet gel formed from a sol containing the polysiloxanecompound having the above-described structure, it will be easier toobtain an aerogel with low thermal conductivity and flexibility. Fromsuch standpoint, in the formula (4) there is mentioned a hydroxyalkylgroup having a carbon number of from 1 to 6 or the like as R₉, and assaid hydroxyalkyl group, there are mentioned a hydroxyethyl group, ahydroxypropyl group, and the like. Also, in the formula (4) there ismentioned an alkylene group having a carbon number of from 1 to 6 or thelike as R₁₀, and as said alkylene group, there are mentioned an ethylenegroup, a propylene group, and the like. Further, in the formula (4) asR₁₁ and R₁₂, there are respectively mentioned an alkyl group having acarbon number of from 1 to 6, a phenyl group, and the like, and as saidalkyl group, there is mentioned a methyl group or the like. In addition,“n” in the formula (4) can be from 2 to 30 and may further be from 5 to20.

Commercial products can be used as the polysiloxane compound having thestructure represented by the general formula (4), which includecompounds such as X-22-160AS, KF-6001, KF-6002, KF-6003 (allmanufactured by Shin-Etsu Chemical Co., Ltd.), XF42-B0970, and FluidOFOH 702-4% (all manufactured by Momentive Performance Materials Inc.).

As the polysiloxane compound having an alkoxy group within a moleculethereof, there is mentioned one having general formula (5) describedbelow. By using the polysiloxane compound having the structurerepresented by the general formula (5), the ladder type structure havingthe bride represented by the general formula (2) described previouslycan be introduced into the skeleton of an aerogel.

In the formula (5), R₁₀ represents an alkyl group or an alkoxy group;R₁₅ and R₁₆ each independently represents an alkoxy group; R¹⁷ and R¹⁸each independently represents an alkyl group or an aryl group; and “in”represents an integer of from 1 to 50. Here, the aryl groups include aphenyl group, a substituted phenyl group, and others. Further, examplesof the substituent in the substituted phenyl group include, an alkylgroup, a vinyl group, a mercapto group, an amino group, a nitro group,and a cyano group. Further, in the formula (5), two or more R₁₄s may,respectively, be identical or different and two or more R₁₆s may,respectively, be identical or different similarly. Still further, in theformula (5), when in is an integer of 2 or more, two or more R₁₇s may,respectively, be identical or different and two or more R₁₈s may,respectively, be identical or different similarly.

By using the wet gel formed from a sol containing the polysiloxanecompound having the above-described structure, it will be easier toobtain an aerogel with low thermal conductivity and flexibility. Fromsuch standpoint, in the formula (5) there are mentioned an alkyl grouphaving a carbon number of from 1 to 6, an alkoxy group having a carbonnumber of from 1 to 6, and the like as R₁₄, and as said alkyl group orsaid alkoxy group, there are mentioned a methyl group, a methoxy group,an ethoxy group, and the like. Also, in the formula (5) as R₁₅ and R₁₆,there are respectively, independently mentioned an alkoxy group having acarbon number of from 1 to 6 and the like, and as said alkoxy group,there are mentioned a methoxy group, an ethoxy group and the like. Also,in the formula (5) as R₁₇ and R₁₈, there are respectively mentioned analkyl group having a carbon number of from 1 to 6, a phenyl group, andthe like, and as said alkyl group, there is mentioned a methyl group orthe like. In addition, “in” in the formula (5) can be from 2 to 30 andmay further be from 5 to 20.

The polysiloxane compound having the structure represented by thegeneral formula (5) can be obtained, for example, by referring to theproduction processes that are reported in Japanese Unexamined PatentPublication No. 2000-26609, Japanese Unexamined Patent Publication No.2012-233110, and others, as appropriate.

Note that because an alkoxy group is hydrolyzed, the polysiloxanecompound having the alkoxy group within a molecule thereof has thepossibility of being present as a hydrolyzed product in a sol and thus,the polysiloxane compound having the alkoxy group within a moleculethereof and its hydrolyzed product may be coexistent. In addition, thealkoxy groups in the molecule may all be hydrolyzed or may be partiallyhydrolyzed in the polysiloxane compound having the alkoxy group within amolecule thereof.

These polysiloxane compounds having reactive groups within moleculesthereof and the hydrolyzed products of said polysiloxane compounds maybe used singly or in combination of two or more kinds.

In preparing the aerogel of the present embodiment, the sol containingthe above-described polysiloxane compound can further comprises at leastone member selected from the group consisting of a silicone compoundhaving a hydrolyzable functional group within a molecule thereof and ahydrolyzed product of said silicone compound. The silicon number withinthe molecule of the silicone compound can be 1 or 2. The siliconecompound having a hydrolyzable functional group is not particularlylimited, but its examples include alkyl silicon alkoxides. Among thealkyl silicon alkoxides, those having the number of hydrolyzablefunctional group being 3 or less can improve water resistance. Examplesof such alkyl silicon alkoxides include methyltrimethoxysilane anddimethyldimethoxysilane. There can also be used silicone compoundshaving the number of the hydrolyzable functional group at molecularterminus thereof being 3 or less, including bistrimethoxysilylmethane,bistrimethoxysilylethane, bistrimethoxysilylhexane,ethyltrimethoxysilane, vinyltrimethoxysilane, and the like. Thesesilicone compounds may be used singly or in combination of two or morekinds.

In addition, the content of the polysiloxane compound and the hydrolyzedproduct of said polysiloxane compound can be from 5 to 50 parts by massand may further be from 10 to 30 parts by mass, based on the total ofthe sol, 100 parts by mass. If it is set at 5 parts by mass or more, itwill be easier to further obtain preferred reactivity; also, if it isset at 50 parts by mass or less, it will be easier to further obtainpreferred compatibility.

Moreover, when the sol further contains the above-described siliconecompound, the ratio of the content of the polysiloxane compound and thehydrolyzed product of said polysiloxane compound to the content of thesilicone compound and the hydrolyzed product of said silicone compoundcan be from 1:0.5 to 1:4 and may further be from 1:1 to 1:2. If theratio between the contents of these compounds is set at 1:0.5 or more,it will be easier to further obtain the preferred compatibility; also,if it is set at 1:4 or less, it will be easier to further suppress theshrinkage of the gel.

The sum of the content of the polysiloxane compound and the hydrolyzedproduct of said polysiloxane compound and the content of the siliconecompound and the hydrolyzed product of said silicone compound can befrom 5 to 50 parts by mass and may further be from 10 to 30 parts bymass, based on the total amount of the sol, 100 parts by mass. If it isset at 5 parts by mass or more, it will be easier to further obtain thepreferred reactivity; also, if it is also set at 50 parts by mass orless, it will be easier to further obtain the preferred compatibility.In so doing, the ratio of the content of the polysiloxane compound andthe hydrolyzed product of said polysiloxane compound to the content ofthe silicone compound and the hydrolyzed product of said siliconecompound can be set within the above-described range.

Production Process for Aerogel>

The process for producing the aerogel will next be described. Theprocess for producing the aerogel is not particularly limited; however,it can be produced according to the process described below, forexample.

Specifically, the aerogel of the present embodiment can be produced by aproduction process principally comprising: a step of forming a sol; astep of forming a wet gel, the step comprising gelling the sol obtainedin the sol forming step and subsequently maturing it to obtain the wetgel; a step of washing and solvent-substituting the wet gel obtained inthe wet gel forming step; and a step of drying comprising drying the wetgel that has been washed and solvent-substituted. Note that the sol is astate prior to causing the gelling reaction and it means, according tothe present embodiment, a state where the polysiloxane compound and/orthe hydrolyzed product of said polysiloxane compound, and optionally,the silicone compound and/or the hydrolyzed product of said siliconecompound are dissolved or dispersed in a solvent. Moreover, the wet gelmeans a gel solid in a wet state having no fluidity while containing aliquid medium.

Each step of the process for producing the aerogel of the presentembodiment will be described hereinbelow.

(Step of Forming Sol)

The step of forming a sol is a step where the polysiloxane compoundand/or the silicone compound is mixed with the solvent and hydrolysis isallowed to form the sol. To accelerate the hydrolysis reaction, an acidcatalyst can further be added to the solvent in the present step. Inaddition, as is illustrated in U.S. Pat. No. 5,250,900, a surfactant anda thermally hydrolyzable compound, and the like can also be added to thesolvent.

As the solvent, there can be used water or a mixed solution of water andan alcohol, for example. The alcohols include methanol, ethanol,n-propanol, 2-propanol, n-butanol, 2-butanol, t-butanol, and the like.Among these, methanol, ethanol, 2-propanol, and the like are mentionedas an alcohol which likely decreases the interface tension against thegel wall and which has low surface tension and a low boiling point.These may be used singly or in a mixture of two or more kinds.

For example, when an alcohol is used as the solvent, the amount of thealcohol can be 4 to 8 moles, may further be 4 to 6.5 moles, and maystill further be 4.5 to 6 moles, based on the total (one mole) of thepolysiloxane compound and the silicone compound. If the amount of thealcohol is set at 4 moles or more, it will be easier to obtain morepreferred compatibility; also, if it is set at 8 moles or less, it willbe easier to suppress the shrinkage of the gel.

The acid catalysts include: inorganic acids such as hydrofluoric acid,hydrochloric acid, nitric acid, sulfuric acid, sulfurous acid,phosphoric acid, phosphorous acid, hypophosphorous acid, bromic acid,chloric acid, chlorous acid, and hypochlorous acid; acid phosphates suchas acid aluminum phosphate, acid magnesium phosphate, and acid zincphosphate; and organic carboxylic acids such as acetic acid, formicacid, propionic acid, oxalic acid, malonic acid, succinic acid, citricacid, malic acid, adipic acid, and azelaic acid. Among these, theorganic carboxylic acids are mentioned as the acid catalyst thatimproves the water resistance of the obtained aerogel more. As saidorganic carboxylic acid, acetic acid may be mentioned but it may beformic acid, propionic acid, oxalic acid, malonic acid, or the like.These may be used singly or in combination of two or more kinds.

Use of the acid catalyst accelerates hydrolysis of the polysiloxanecompound and the silicone compound and, thus, allows the sol to beobtained in a shorter time.

The added amount of the acid catalyst can be from 0.001 to 0.1 parts bymass relative to the total amount, 100 parts by mass, of thepolysiloxane compound and the silicone compound.

Non-ionic surfactants, ionic surfactants, and the like can be used assurfactants. These may be used singly or in combination of two or morekinds.

As the non-ionic surfactant, there can be used, for example, onescontaining a hydrophilic portion such as polyoxyethylene and ahydrophobic portion principally consisting of an alkyl group and onescontaining a hydrophilic portion such as polyoxypropylene. As the onecontaining a hydrophilic portion such as polyoxyethylene and ahydrophobic portion principally consisting of an alkyl group, there arementioned polyxoyethylenenonyl phenyl ether, polyoxyethyleneoctyl phenylether, polyoxyethylene alkyl ether, and the like. As the one containinga hydrophilic portion such as polyoxypropylene, there are mentionedpolyoxypropylenealkyl ether and a block copolymer of polyoxyethylenewith polyoxypropylene.

The ionic surfactants include a cationic surfactant, an anionicsurfactant, an amphoteric surfactant, and the like. The cationicsurfactants include bromocetyltrimethyl ammonium, chlorocetyltrimethylammonium, and the like; and the anionic surfactants include sodiumdodecyl sulfonate, and the like. Also, the amphoteric surfactantsinclude an amino acid type surfactant, a betaine type surfactant, anamine oxide type surfactant, and the like. Examples of the amino acidtype surfactant include acylglutamic acid. Examples of the betaine typesurfactant include lauryldimethylaminoacetic acid betaine andstearyldimethylaminoacetic acid betaine. Examples of the amine oxidetype surfactant include lauryldimethylamine oxide.

These surfactants bring a small differential chemical affinity betweenthe solvent in the reaction system and the growing siloxane polymer andfunction to suppress phase separation in the step of forming a wet gelwhich will be described later.

The added amount of the surfactant depends on the type of the surfactantor the types of the polysiloxane compound and the silicone compound aswell as on their amounts; however, it can be, for example, from 1 to 100parts by mass and may further be from 5 to 60 parts by mass, based onthe total amount, 100 parts by mass, of the polysiloxane compound andthe silicone compound

The thermally hydrolyzable compound generates a base catalyst throughthermal hydrolysis, causes the reaction solution to be basic, andaccelerates a sol/gel reaction in the step of forming a wet gel whichwill be described later. Hence, this thermally hydrolyzable compound isnot particularly limited as long as it is a compound capable of causingthe reaction solution to be basic after the hydrolysis. There arementioned urea; acid amides such as formamide, N-methylformamide,N,N-dimethylformamide, acetoamide, N-methylacetoamide, and N,N-dimethylacetoamide; and cyclic nitrogen compounds such ashexamethylenetetramine Among these, urea likely allows theabove-described acceleration effect to be obtained particularly.

The added amount of the thermally hydrolyzable compound is notparticularly limited as long as it is a amount capable of sufficientlyaccelerating a sol/gel reaction in the step of forming a wet gel whichwill be descried later. For example, when urea is used as the thermallyhydrolyzable compound, the amount of its addition can be from 1 to 200parts by mass and may further be from 1 to 50 parts by mass, based onthe total amount, 100 parts by mass, of the polysiloxane compound andthe silicone compound. If the added amount is set at 1 mass part ormore, it will be easier to obtain preferred reactivity; also, if theadded amount is set at 200 parts by mass or less, it will be easier tosuppress the precipitation of crystals as well as suppress a decrease inthe gel density.

The hydrolysis in the step of forming a sol depends on the types andamounts of the polysiloxane compound, the silicone compound, the acidcatalyst, the surfactant, and the like in the mixed solution; however,it may, for example, be conducted for 10 minutes to 24 hours under atemperature condition of from 20 to 60° C. and for 5 minutes to 8 hoursunder a temperature condition of from 50 to 60° C. Thereby, thehydrolyzable functional groups in the polysiloxane compound and thesilicone compound are sufficiently hydrolyzed, and there can be moresecurely obtained the hydrolyzed product of the polysiloxane compoundand the hydrolyzed product of the silicone compound.

Notwithstanding, when the thermally hydrolyzable compound is added tothe solvent, the temperature condition in the step of forming a sol maybe adjusted to a temperature that suppresses the hydrolysis of thethermally hydrolyzable compound as well as suppresses the gelation ofthe sol. The temperature in this instance may be any temperature as longas it is a temperature capable of suppressing the hydrolysis of thethermally hydrolyzable compound. For example, when urea is used as thethermally hydrolyzable compound, the temperature condition in the stepof forming a sol can be from 0 to 40° C. and may further be from 10 to30° C.

(Step of Forming Wet Gel)

The step of forming a wet gel is a step which gelatinizes the solobtained in the step of forming a sol and subsequently matures it toproduce the wet gel. A base catalyst can be used in the present step toaccelerate the gelation.

The base catalysts include: alkaline metal hydroxides such as lithiumhydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide;ammonium compounds such as ammonium hydroxide, ammonium fluoride,ammonium chloride, and ammonium bromide; basic sodium phosphate saltssuch as sodium metaphosphate, sodium pyrophosphate, and sodiumpolyphosphate; aliphatic amines such as allylamine, diallylamine,triallylamine, isopropylamine, diisopropylamine, ethylamine,diethylamine, triethylamine, 2-ethylhexylamine, 3-ethoxypropylamine,diisobutylamine, 3-(diethylamino)propylamine, di-2-ethylhexylamine,3-(dibutylamino)propylamine, tetramethylethylenediamine, t-butylamine,sec-butylamine, propylamine, 3-(methylamino)propylamine,3-(dimethylamino)propylamine, 3-methoxyamine, dimethylethanolamine,methyldiethanolamine, diethanolamine, and triethanolamine; andnitrogen-containing heterocyclic compounds such as morpholine,N-methylmorpholine, 2-methylmorpholine, piperazine and a derivativethereof, piperizine and a derivative thereof, and imidazole and aderivative thereof. Among these, ammonium hydroxide (ammonia water) isexcellent from the standpoint that because its volatility is high and ithardly remains in the aerogel after drying, it does not impair waterresistance as well as more from the standpoint of economic efficiency.The base catalysts may be used singly or in combination of two or morekinds.

By using the base catalyst, it will be possible to accelerate adehydration/condensation reaction and dealcoholization/condensationreaction of the polysiloxane compound and/or the hydrolyzed product ofthe polysiloxane compound as well as the silicone compound and/or thehydrolyzed product of the silicone compound in the sol and to carry outthe gelation of the sol in a shorter time. This also allows a wet gelhaving a higher strength (rigidity) to be obtained. Especially, ammoniahas high volatility and hardly remains in the aerogel; therefore, ifammonia is used as the base catalyst, it will be possible to obtain anaerogel having more excellent water resistance.

The added amount of the base catalyst can be from 0.5 to 5 parts by massand may further be from 1 to 4 parts by mass, based on the total amount,100 parts by mass, of the polysiloxane compound and the siliconecompound. If the added amount is set at 0.5 parts by mass or more, itwill be possible to carry out the gelation in a shorter time; if theadded amount is set at 5 parts by mass or less, it will be possible tosuppress a decrease in water resistance more.

The gelation of the sol in the step of forming a wet gel may beconducted in a sealed container so that the solvent and the basecatalyst may not evaporate. The temperature of gelation can be from 30to 90° C. and may further be from 40 to 80° C. If the temperature ofgelation is set at 30° C. or higher, the gelation can be conducted in ashorter time and a wet gel having higher strength (rigidity) can beobtained. Further, if the temperature of gelation is set at 90° C. orlower, it will allow the evaporation of the solvent (especially,alcohols) to be easily suppressed, and thus, the gelation can be causedwhile the volume shrinkage is suppressed.

Maturation in the step of forming a wet gel may be conducted in a sealedcontainer so that the solvent and the base catalyst may not evaporate.Because of the maturation, bonding of the components constituting thewet gel will be strong; and consequently, it will be possible to obtaina wet gel having high strength (rigidity) that is sufficient to suppressthe shrinkage during drying. The temperature of maturation can be 30 to90° C. and may further be 40 to 80° C. If the temperature of maturationis set at 30° C. or higher, it will be possible to obtain a wet gelhaving higher strength (rigidity). Also, if the temperature ofmaturation is set at 90° C. or lower, it will allow the evaporation ofthe solvent (especially, alcohols) to be easily suppressed, and thus,the gelation can be caused while the volume shrinkage is suppressed.

Further, because there are cases where it is difficult to judge thepoint at which the gelation of the sol is complete, the gelation of thesol and the subsequent maturation may be conducted continuously in aseries of manipulations.

The time of gelation and the time of maturation differ depending on thetemperature of gelation and the temperature of maturation; however, whenthe time of gelation and the time of maturation are totaled, it can be 4to 480 hours and may further be 6 to 120 hours. If the total of the timeof gelation and the time of maturation is set at 4 hours or more, itwill be possible to obtain a wet gel having higher strength (rigidity);if it is set at 480 hours or less, it will be easier to maintain theeffects of the maturation.

In order that the density of the aerogel to be obtained should belowered and the average pore diameter of the aerogel to be obtainedshould be made large, the temperature of gelation and the temperature ofmaturation can be heightened within the above-described range and thetotal of the time of gelation and the time of maturation can belengthened within the above-described range. Additionally, in order thatthe density of the aerogel to be obtained should be heightened and theaverage pore diameter of the aerogel to be obtained should be madesmall, the temperature of gelation and the temperature of maturation canbe lowered within the above-described range and the total of the time ofgelation and the time of maturation can be shortened within theabove-described range.

(Step of Washing and Solvent-Substituting)

The step of washing and solvent-substituting is a step having a step ofwashing (washing step) a wet gel obtained in the step of forming a wetgel as described above and a step of substituting (solvent-substitutingstep) a washing liquid in the wet gel with a solvent that is suitablefor drying conditions (drying step to be described later). The step ofwashing and solvent-substituting is feasible even in the form of onlycarrying out the step of solvent-substituting without carrying out thestep of washing a wet gel; however, the wet gel may be washed from thestandpoint of reducing impurities such as unreacted products andby-products in the wet gel and enabling the production of an aerogelwith higher purity.

The washing step washes the wet gel obtained in the step of forming awet gel. Said washing can be, for example, carried out repeatedly usingwater or an organic solvent. In so doing, heating can improve washingefficiency.

As the organic solvent, there can be used a variety of organic solvents,including methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, acetone,methyl ethyl ketone, 1,2-dimethoxyethane, acetonitrile, hexane, toluene,diethyl ether, chloroform, ethyl acetate, tetrahydrofuran,methylenechloride, N,N-dimethylformamide, dimethyl sulfoxide, aceticacid, formic acid, and the like. The organic solvents may be used singlyor in a mixture of two or more kinds.

In order to suppress the shrinkage of the gel through drying, a solventwith low surface tension can be used in the step of solvent-substitutingwhich will be described later. However, the solvent with low surfacetension generally has extremely low mutual solubility with water.Therefore, if the solvent with low surface tension is used in the stepof solvent-substituting, the organic solvents to be used in the stepinclude hydrophilic organic solvents having high mutual solubilitiestoward both of water and the solvent with low surface tension. Further,the hydrophilic organic solvent for use in the step of washing can playa role of preliminary substitution for the sake of the step ofsolvent-substituting. Among the organic solvents, the hydrophilicorganic solvents include methanol, ethanol, 2-propanol, acetone, methylethyl ketone, and the like. In addition, methanol, ethanol, methyl ethylketone, and the like are excellent from the standpoint of economicefficiency.

The amount of water or the organic solvent to be used in the step ofwashing can be an amount capable of substituting and washing the solventin the wet gel sufficiently. Said amount can be from 3 to 10 times thevolume of the wet gel. Washing can be repeated until the water contentin the wet gel after the washing reaches 10% by mass or less relative tothe mass of silica.

The temperature environment in the step of washing can be a temperaturebelow the boiling point of the solvent to be used in the washing. Forexample, when methanol is used, heating is set at the level of from 30to 60° C.

In the step of solvent-substituting, the solvent in the washed wet gelis substituted with a prescribed solvent for substitution to suppressthe shrinkage in the step of drying which will be described later. In sodoing, heating can improve the efficiency of substitution. The solventswith low surface tension to be described later are specificallymentioned as the solvent for substitution when drying in the step ofdrying is conducted at a temperature of less than the critical point ofthe solvent to be used for drying under atmospheric pressure. On theother hand, when supercritical drying is conducted, examples of thesolvent for substitution include ethanol, methanol, 2-propanol,dichlorodifluoroethane, carbon dioxide, and a mixed solvent of two ormore of the foregoing.

As the solvent with low surface tension, there are mentioned thosehaving a surface tension of 30 mN/m or less at 20° C. Further, saidsurface tension may be 25 mN/m or less and may even be 20 mN/m or less.Examples of the solvent with low surface tension include aliphatichydrocarbons such as pentane (15.5), hexane (18.4), heptane (20.2),octane (21.7), 2-methylpentane (17.4), 3-methylpentane (18.1),2-methylhexane (19.3), cyclopentane (22.6), cyclohexane (25.2), and1-pentene (16.0); aromatic hydrocarbons such as benzene (28.9), toluene(28.5), m-xylene (28.7), and p-xylene (28.3); halogenated hydrocarbonssuch as dichloromethane (27.9), chloroform (27.2), carbon tetrachloride(26.9), 1-chloropropane (21.8), and 2-chloropropane (18.1); ethers suchas ethyl ether (17.1), propyl ether (20.5), isopropyl ether (17.7),butyl ethyl ether (20.8), and 1,2-dimethoxyethane (24.6); ketones suchas acetone (23.3), methyl ethyl ketone (24.6), methyl propyl ketone(25.1), and diethyl ketone (25.3); and esters such as methyl acetate(24.8), ethyl acetate (23.8), propyl acetate (24.3), isopropyl acetate(21.2), isobutyl acetate (23.7), and ethyl butyrate (24.6). In theparentheses, the surface tensions at 25° C. are shown and their unitsare mN/m. Among these, the aliphatic hydrocarbons (e.g., hexane andheptane) have low surface tension as well as excellent work environmentadaptability. Also, if the hydrophilic organic solvents such as acetone,methyl ethyl ketone, 1,2-dimethoxyethane, and the like are used out ofthese, they can serve as the organic solvent in the step of washing stepas well. Further, ones which have boiling points of 100° C. or lessunder normal pressure may be used out of these from the standpoint thatdrying in the step of drying as described later is easy. The organicsolvents may be used singly or in a mixture of two or more kinds.

The amount of the solvent to be used in the step of solvent-substitutingcan be an amount capable of sufficiently substituting the solvent in thewet gel after drying. Said amount can be from 3 to 10 times the volumeof the wet gel.

The temperature environment in the step of solvent-substituting can be atemperature below the boiling point of the solvent to be used in thesubstitution. For example, when heptane is used, heating is set at thelevel of from 30 to 60° C.

(Drying Step)

The step of drying dries a wet gel that has been washed andsolvent-substituted as described later. This allows the aerogel to befinally obtained.

The technique of drying is not particularly limited, and there can beused normal pressure drying, supercritical drying or freeze-drying, eachof which is known in the art. Among these, the normal pressure drying orthe supercritical drying can be used from the standpoint that an aerogelwith low density is easily produced. Also, from the standpoint ofenabling production at low costs, the normal pressure drying can beused. Note that the normal pressure in the present embodiments means 0.1MPa (atmospheric pressure).

The aerogel of the present embodiment can be obtained by drying the wetgel that has been washed and solvent-substituted at a temperature ofless than the critical temperature of the solvent to be used in dryingunder atmospheric pressure. The temperature of drying differs dependingon the type of the solvent substituted but can be from 20 to 80° C. inconsideration of the point that there are cases where drying at hightemperatures especially accelerates the rate of evaporation of thesolvent to generate large cracks in the gel. Moreover, said temperatureof drying may further be from 30 to 60° C. In addition, the time ofdrying differs depending on the volume of the wet gel and thetemperature of drying but can be from 4 to 120 hours. Note thataccording to the present embodiments, the normal pressure dryingencompasses speeding up drying by application of pressure in the rangewithin which productivity is not obstructed.

The aerogel of the present embodiment can also be obtained by supercritically drying the wet gel that has been washed andsolvent-substituted. The supercritical drying can be conducted with thetechniques that are known in the art. As the method of supercriticaldrying, there is, for example, mentioned a method by which the solventis removed at a temperature of not less than the critical temperature ofthe solvent contained in the wet gel. Alternatively, as the method ofsupercritical drying, there is mentioned a method comprising: immersingthe wet gel in liquidated carbon dioxide under the conditions, forexample, on the orders of from 20 to 25° C. and from 5 to 20 MPa;thereby substituting the whole or part of the solvent contained in thewet gel with carbon dioxide with its critical point being lower that ofsaid solvent; and then removing the carbon dioxide itself or a mixtureof the carbon dioxide and the solvent.

The aerogel obtained by the normal pressure drying or the supercriticaldrying thus mentioned may further be additionally dried at from 105 to200° C. for about 0.5 to 2 hours under normal pressure. This allows anaerogel having low density and small pores to be more easily obtained.The additional drying can be carried out at from 1 to 50 to 200° C.under normal pressure.

The aerogels of the present embodiments that are obtained through thesteps thus far mentioned have thermal conductivities of 0.03 W/m·K orless and compressive elasticity moduli of 2 MPa or less at 25° C. underatmospheric pressure, as well as possess excellent thermal insulationand productivities that are unattainable by the aerogels in the priorart. Considering these advantages, the application can be in the usagesas thermal insulating materials in the construction field, automobilefield, consumer electronics, semiconductor field, industrial facilities,and others. The aerogels of the present embodiments can be utilized asadditives for paints, cosmetics, anti-blocking agents, catalystsupports, and others in addition to the usage as thermal insulatingmaterials.

EXAMPLES

The present invention will be next described by way of the examplesbelow in more detail; however, these examples are not intended to limitthe present invention.

Preparation of Aerogels Example 1

Forty (40.0) parts by mass of carbinol-modified siloxane represented bythe general formula (4) “X-22-160AS” (product name: manufactured byShin-Etsu Chemical Co., Ltd.) as a polysiloxane compound, 60.0 parts bymass of methyltrimethoxysilane “LS-530” (product name; abbreviated as“MTMS” hereafter: manufactured by Shin-Etsu Chemical Co., Ltd.) as asilicone compound, 120.0 parts by mass of water, and 80.0 parts by massof methanol were mixed. To this was added 0.10 parts by mass of aceticacid as an acid catalyst, and reaction was allowed at 25° C. for 8 hoursto obtain a sol. To the obtained sol was added 40.0 parts by mass ofammonia water with a concentration of 5%. After gelation at 60° C. for 8hours, it was matured at 80° C. for 48 hours to obtain a wet gel. Theobtained wet gel was then immersed in 2500.0 parts by mass of methanol,and washing was carried out at 60° C. over 12 hours. This washingmanipulation was carried out three times while the methanol wasexchanged for fresh methanol. The washed wet gel was next immersed in2500.0 parts by mass of heptane as a low surface tension solvent, andsolvent substitution was carried out at 60° C. over 12 hours. Thismanipulation of solvent substitution was carried out three times whilethe heptane was exchanged for fresh heptane. The wet gel that had beenwashed and solvent-substituted was dried at 40° C. for 96 hours undernormal pressure; thereafter, it was further dried at 150° C. for 2 hoursto obtain Aerogel 1 having the structure represented by the generalformula (1).

Example 2

Forty (40.0) parts by mass of X-22-16 represented by the general formula(4) as a polysiloxane compound, 60.0 parts by mass of MTMS as a siliconecompound, 120.0 parts by mass of water, and 80.0 parts by mass ofmethanol were mixed. To this were added 0.10 parts by mass of aceticacid as an acid catalyst, and 20.0 parts by mass ofcetyltrimethylammonium bromide (manufactured by Wako Pure ChemicalIndustries, Ltd.: abbreviated as “CTAB” hereafter) as a cationicsurfactant; and reaction was allowed at 25° C. for 8 hours to obtain asol. Thereafter, Aerogel 2 having the structure represented by thegeneral formula (1) was obtained in a similar manner to Example 1.

Example 3

Two hundred (200.0) parts by mass of water, 0.10 parts by mass of aceticacid as an acid catalyst, 20.0 parts by mass of CTAB as a cationicsurfactant, and 120.0 parts by mass of urea as a thermally hydrolyzablecompound were mixed. To this were added 40.0 parts by mass of X-22-160ASrepresented by the general formula (4) as a polysiloxane compound and60.0 parts by mass of MTMS as a silicone compound; and reaction wasallowed at 25° C. for 2 hours to obtain a sol. After gelation at 60° C.for 8 hours, the obtained sol was matured at 80° C. for 48 hours toobtain a wet gel. Thereafter, Aerogel 3 having the structure representedby the general formula (1) was obtained in a similar manner to Example1.

Example 4

Two hundred (200.0) parts by mass of water, 0.10 parts by mass of aceticacid as an acid catalyst, 20.0 parts by mass of “F-127,” which is ablock copolymer of polyoxyethylene and polyoxypropylene (product name:manufactured by BASF), as a non-ionic surfactant, and 120.0 parts bymass of urea as a thermally hydrolyzable compound were mixed. To thiswere added 40.0 parts by mass of X-22-160AS represented by the generalformula (4) as a polysiloxane compound, and 60.0 parts by mass of MTMSas a silicone compound; and reaction was allowed at 25° C. for 2 hoursto obtain a sol. After gelation at 60° C. for 8 hours, the obtained solwas matured at 80° C. for 48 hours to obtain a wet gel. Thereafter,Aerogel 4 having the structure represented by the general formula (1)was obtained in a similar manner to Example 1.

Example 5

Two hundred (200.0) parts by mass of water, 0.10 parts by mass of aceticacid as an acid catalyst, 20.0 parts by mass of CTAB as a cationicsurfactant, and 120.0 parts by mass of urea as a thermally hydrolyzablecompound were mixed. To this were added 20.0 parts by mass of X-22-160ASrepresented by the general formula (4) as a polysiloxane compound and80.0 parts by mass of MTMS as a silicone compound; and reaction wasallowed at 25° C. for 2 hours to obtain a sol. After gelation at 60° C.for 8 hours, the obtained gel was matured at 80° C. for 48 hours toobtain a wet gel. Thereafter, Aerogel 5 having the structure representedby the general formula (1) was obtained in a similar manner to Example1.

Example 6

Two hundred (200.0) parts by mass of water, 0.10 parts by mass of aceticacid as an acid catalyst, 20.0 parts by mass of CTAB as a cationicsurfactant, and 120.0 parts by mass of urea as a thermally hydrolyzablecompound were mixed. To this were added 40.0 parts by mass of apolysiloxane compound having both termini modified with two alkoxyfunctionalities represented by the general formula (5) (hereafterreferred to as “polysiloxane compound A) as a polysiloxane compound and60.0 parts by mass of MTMS as a silicone compound; and reaction wasallowed at 25° C. for 2 hours to obtain a sol. After gelation at 60° C.for 8 hours, the obtained sol was matured at 80° C. for 48 hours toobtain a wet gel. Thereafter, Aerogel 6 having a ladder type structurewhich comprises the structures represented by the general formulas (2)and (3) was obtained in a similar manner to Example 1.

Note that the “polysiloxane compound A” was synthesized in the followingmanner. In a 1-liter flask having three necks that was provided with astirrer, a thermometer and a Dimroth condenser, 100.0 parts by mass ofhydroxy-terminated dimethylpolysiloxane “XC96-723” (product name:Momentive Performance Materials Inc.), 181.3 parts by mass ofmethyltrimethoxysilane, and 0.50 parts by mass of t-butylamine weremixed; and reaction was allowed at 30° C. for 5 hours. This reactionsolution was then heated at 140° C. for 2 hours under a reduced pressureof 1.3 kPa to remove volatile portions, whereby the polysiloxanecompound having both termini modified with two alkoxy functionalities(polysiloxane compound A) was obtained.

Example 7

Two hundred (200.0) parts by mass of water, 0.10 parts by mass of aceticacid as an acid catalyst, 20.0 parts by mass of CTAB as a cationicsurfactant, and 120.0 parts by mass of urea as a thermally hydrolyzablecompound were mixed. To this were added 20.0 parts by mass of thepolysiloxane compound A represented by the general formula (5) as apolysiloxane compound and 80.0 parts by mass of MTMS as a siliconecompound; and reaction was allowed at 25° C. for 2 hours to obtain asol. After gelation at 60° C. for 8 hours, the obtained sol was maturedat 80° C. for 48 hours to obtain a wet gel. Thereafter, Aerogel 7 havingladder type structures represented by the general formulas (2) and (3)was obtained in a similar manner to Example 1.

Example 8

Two hundred (200.0) parts by mass of water, 0.10 parts by mass of aceticacid as an acid catalyst, 20.0 parts by mass of CTAB as a cationicsurfactant, and 120.0 parts by mass of urea as a thermally hydrolyzablecompound were mixed. To this were added 20.0 parts by mass of X-22-160ASrepresented by the general formula (4) as a polysiloxane compound and60.0 parts by mass of MTMS, and 20.0 parts by mass ofbistrimethoxysilylhexane as silicone compounds; and reaction was allowedat 25° C. for 2 hours to obtain a sol. After gelation at 60° C. for 8hours, the obtained sol was matured at 80° C. for 48 hours to obtain awet gel. Thereafter, Aerogel 8 having the structure represented by thegeneral formula (1) was obtained in a similar manner to Example 1.

Example 9

Two hundred (200.0) parts by mass of water, 0.10 parts by mass of aceticacid as an acid catalyst, 20.0 parts by mass of CTAB as a cationicsurfactant, and 120.0 parts by mass of urea as a thermally hydrolyzablecompound were mixed. To this were added 20.0 parts by mass of thepolysiloxane compound A represented by the general formula (5) as apolysiloxane compound, 60.0 parts by mass of MTMS, and 20.0 parts bymass of bistrimethoxysilylhexane as silicone compounds; and reaction wasallowed at 25° C. for 2 hours to obtain a sol. After gelation at 60° C.for 8 hours, the obtained sol was matured at 80° C. for 48 hours toobtain a wet gel. Thereafter, Aerogel 9 having ladder type structuresrepresented by the general formulas (2) and (3) was obtained in asimilar manner to Example 1.

Example 10

Two hundred (200.0) parts by mass of water, 0.10 parts by mass of aceticacid as an acid catalyst, 20.0 parts by mass of CTAB as a cationicsurfactant, and 120.0 parts by mass of urea as a thermally hydrolyzablecompound were mixed. To this were added 20.0 parts by mass of X-22-160ASrepresented by the general formula (4) and 20.0 parts by mass of thepolysiloxane compound A represented by the general formula (5) aspolysiloxane compounds, and 60.0 parts by mass of MTMS as a siliconecompound; and reaction was allowed at 25° C. for 2 hours to obtain asol. After gelation at 60° C. for 8 hours, the obtained sol was maturedat 80° C. for 48 hours to obtain a wet gel. Thereafter, Aerogel 10having the structure represented by the general formula (1) as well asthe ladder type structures represented by the general formulas (2) and(3) was obtained in a similar manner to Example 1.

Example 11

Two hundred (200.0) parts by mass of water, 0.10 parts by mass of aceticacid as an acid catalyst, 20.0 parts by mass of CTAB as a cationicsurfactant, and 120.0 parts by mass of urea as a thermally hydrolyzablecompound were mixed. To this were added 40.0 parts by mass of X-22-160ASrepresented by the general formula (4) as a polysiloxane compound and60.0 parts by mass of MTMS as a silicone compound; and reaction wasallowed at 25° C. for 2 hours to obtain a sol. After gelation at 60° C.for 8 hours, the obtained sol was matured at 80° C. for 48 hours toobtain a wet gel. The obtained wet gel was then immersed in 2500.0 partsby mass of methanol, and washing was carried out at 60° C. over 12hours. This washing manipulation was carried out three times while themethanol was exchanged for fresh methanol. The washed wet gel was nextimmersed in 2500.0 parts by mass of 2-propanol, and solvent substitutionwas carried out at 60° C. over 12 hours. This manipulation of solventsubstitution was carried out three times while the 2-propanol wasexchanged for fresh 2-propanol.

Next, super critical drying of the solvent-substituted wet gel wascarried out. An autoclave was filled with 2-propanol, and thesolvent-substituted wet gel was charged therein. Further, liquefiedcarbon dioxide was fed in the autoclave to fill the inside of theautoclave with a mixture of 2-propanol and carbon dioxide as adispersion medium. Heat and pressure were then applied to the autoclaveso that its interior environment were 80° C. and 14 MPa, and aftersufficiently circulating supercritical carbon dioxide within theautoclave, the pressure was reduced to remove 2-propanol and carbondioxide contained in the gel. Thus, Aerogel 11 having the structurerepresented by the general formula (1) was obtained.

Example 12

Two hundred (200.0) parts by mass of water, 0.10 parts by mass of aceticacid as an acid catalyst, 20.0 parts by mass of CTAB as a cationicsurfactant, and 120.0 parts by mass of urea as a thermally hydrolyzablecompound were mixed. To this were added 40.0 parts by mass of thepolysiloxane compound A represented by the general formula (5) as apolysiloxane compound and 60.0 parts by mass of MTMS as a siliconecompound; and reaction was allowed at 25° C. for 2 hours to obtain asol. After gelation at 60° C. for 8 hours, the obtained sol was maturedat 80° C. for 48 hours to obtain a wet gel. Thereafter, Aerogel 12having ladder type structures represented by the general formulas (2)and (3) was obtained in a similar manner to Example 11.

Example 13

Two hundred (200.0) parts by mass of water, 0.10 parts by mass of aceticacid as an acid catalyst, 20.0 parts by mass of CTAB as a cationicsurfactant, and 120.0 parts by mass of urea as a thermally hydrolyzablecompound were mixed. To this were added 40.0 parts by mass of apolysiloxane compound having both termini modified with three alkoxyfunctionalities represented by the general formula (5) (hereafterreferred to as “polysiloxane compound B) as a polysiloxane compound and60.0 parts by mass of MTMS as a silicone compound; and reaction wasallowed at 25° C. for 2 hours to obtain a sol. After gelation at 60° C.for 8 hours, the obtained sol was maturated at 80° C. for 48 hours toobtain a wet gel. Thereafter, Aerogel 13 was obtained in a similarmanner to Example 1.

Note that the “polysiloxane compound B” was synthesized in the followingmanner. First, in a 1-liter flask having three necks that was providedwith a stirrer, a thermometer and a Dimroth condenser, 100.0 parts bymass of XC96-723, 202.6 parts by mass of tetramethoxysilane, and 0.50parts by mass of t-butylamine were mixed; and reaction was allowed at30° C. for 5 hours. This reaction solution was then heated at 140° C.for 2 hours under a reduced pressure of 1.3 kPa to remove volatileportions, whereby the polysiloxane compound having both termini modifiedwith three alkoxy functionalities (polysiloxane compound B) wasobtained.

Example 14

Two hundred (200.0) parts by mass of water, 0.10 parts by mass of aceticacid as an acid catalyst, 20.0 parts by mass of CTAB as a cationicsurfactant, and 120.0 parts by mass of urea as a thermally hydrolyzablecompound were mixed. To this were added 20.0 parts by mass of thepolysiloxane compound B represented by the general formula (5) as apolysiloxane compound and 80.0 parts by mass of MTMS as a siliconecompound; and reaction was allowed at 25° C. for 2 hours to obtain asol. After gelation at 60° C. for 8 hours, the obtained sol was maturedat 80° C. for 48 hours to obtain a wet gel. Thereafter, Aerogel 14 wasobtained in a similar manner to Example 1.

Comparative Example 1

Two hundred (200.0) parts by mass of water, 0.10 parts by mass of aceticacid as an acid catalyst, 20.0 parts by mass of CTAB as a cationicsurfactant, and 120.0 parts by mass of urea as a thermally hydrolyzablecompound were mixed. To this was added 100.0 parts by mass of MTMS as asilicone; and reaction was allowed at 25° C. for 2 hours to obtain asol. After gelation at 60° C. for 8 hours, the obtained sol was maturedat 80° C. for 48 hours to obtain a wet gel. Thereafter, Aerogel 15 wasobtained in a similar manner to Example 1.

Comparative Example 2

Two hundred (200.0) parts by mass of water, 0.10 parts by mass of aceticacid as an acid catalyst, 20.0 parts by mass of CTAB as a cationicsurfactant, and 120.0 parts by mass of urea as a thermally hydrolyzablecompound were mixed. To this were added 70.0 parts by mass of MTMS and30.0 parts by mass of dimethyldimethoxysilane “LS-520” (product name;abbreviated as “DMDMS” hereafter: manufactured by Shin-Etsu ChemicalCo., Ltd.) as silicone compounds; and reaction was allowed at 25° C. for2 hours to obtain a sol. After the gelation at 60° C. for 8 hours, theobtained sol was matured at 80° C. for 48 hours to obtain a wet gel.Thereafter, Aerogel 16 was obtained in a similar manner to Example 1.

Comparative Example 3

Two hundred (200.0) parts by mass of water, 0.10 parts by mass of aceticacid as an acid catalyst, 20.0 parts by mass of CTAB as a cationicsurfactant, and 120.0 parts by mass of urea as a thermally hydrolyzablecompound were mixed. To this were added 60.0 parts by mass of MTMS and40.0 parts by mass of DMDMS as silicone compounds; and reaction wasallowed at 25° C. for 2 hours to obtain a sol. After gelation at 60° C.for 8 hours, the obtained sol was matured at 80° C. for 48 hours toobtain a wet gel. Thereafter, Aerogel 17 was obtained in a similarmanner to Example 1.

Comparative Example 4

Two hundred (200.0) parts by mass of water, 0.10 parts by mass of aceticacid as an acid catalyst, 20.0 parts by mass of CTAB as a cationicsurfactant, 120.0 parts by mass of urea as a thermally hydrolyzablecompound were mixed. To this was added 100.0 parts by mass of MTMS as asilicone compound; and reaction was allowed at 25° C. for 2 hours toobtain a sol. After gelation at 60° C. for 8 hours, the obtained sol wasmatured at 80° C. for 48 hours to obtain a wet gel. Thereafter, Aerogel18 was obtained in a similar manner to Example 1.

Drying methods and Si starting materials (polysiloxane compounds andsilicone compounds) in the respective Examples and Comparative Examplesare altogether shown in Table 1.

[Various Evaluations]

As for Aerogels 1-18 obtained in the respective Examples and ComparativeExamples, the thermal conductivities, compressive elasticity moduli,maximum compressive deformation rates, recovery rates from deformation,signal area ratios of silicon-containing bonding units Q, T, and D,densities, and porosities were measured under the conditions describedbelow and were evaluated. The results of evaluations are altogethershown in Table 2.

(1) Measurement of Thermal Conductivity

By using a blade with an edge angle of from about 20 to about 25degrees, the aerogel was processed into a size of from 150×150×100 mm³to make a sample for measurement. If necessary, the sample formeasurement was next shaped with sandpaper of #1500 and above to securethe parallelism of surfaces. Prior to the measurement of thermalconductivity, the constant temperature drying oven “DVS402” (productname: manufactured by Yamato Scientific Co. Ltd.) was used to dry theobtained sample for measurement at 100° C. for 30 minutes underatmospheric pressure. The sample for measurement was next transferredinto a desiccator and was cooled to 25° C.

The measurement of thermal conductivity was carried out using the steadystate thermal conductivity measuring device “HFM436Lamda” (product name:manufactured by NETZSCH GmbH & Co.). The measurement conditions were atan average temperature of 25° C. and under atmospheric pressure. Thesample for measurement obtained as described above was sandwichedbetween an upper heater and a lower heater at a load of 0.3 MPa to set atemperature differential ΔT of 20° C. and was adjusted such thatone-dimensional heat flow was formed by a guard heater, while the uppersurface temperature and the lower surface temperature of the sample formeasurement were measured. Thermal resistance R_(S) of the sample formeasurement was then determined according to the following equation:

R _(S) =N((T _(U) −T _(L))/Q)−R _(O)

wherein T_(U) represents an upper surface temperature of the sample formeasurement; T_(L) represents a lower surface temperature of the samplefor measurement; R_(O) represents a contact thermal resistance of aninterface between the upper and lower surfaces; and Q represents anoutput of a heat flux meter. Note that N was a proportionalitycoefficient and was determined in advance by using a calibration sample.

Thermal conductivity λ of the sample for measurement was determined fromthe obtained thermal resistance R_(S) according to the followingequation:

λ=d/R _(S)

wherein “d” represents a thickness of the sample for measurement.

(2) Measurement of Compressive Elasticity Modulus, Maximum CompressiveDeformation Rate, and Recovery Rate from Deformation

By using a blade with an edge angle of from about 20 to about 25degrees, the aerogel was processed into a cube of 7.0 mm square (in diceform) to make a sample for measurement. If necessary, the sample formeasurement was next shaped with sandpaper of #1500 and above to securethe parallelism of surfaces. Prior to the measurement of thermalconductivity, the constant temperature drying oven “DVS402” (productname: manufactured by Yamato Scientific Co. Ltd.) was used to dry thesample for measurement at 100° C. for 30 minutes under atmosphericpressure. The sample for measurement was next transferred into adesiccator and was cooled to 25° C.

The small size desk top type tester “EZTest” (product name: ShimadzuCorporation) was used as the measuring device. Further, one with 500 Nwas used as a load cell. Also, an upper platen (ϕ 20 mm) and a lowerplaten (ϕ 118 mm), both of which were made of stainless steel, were usedas compression measuring jigs. The sample for measurement was setbetween the upper platen and the lower platen that were arranged inparallel, and compression was carried out at a rate of 1 mm/min. Thetemperature for measurement was set at 25° C., and the measurement wascaused to end at a point that a load exceeding 500 N was applied or thesample for measurement was destroyed. Here, strain ε was determinedaccording to the following equation:

ε=Δd/d1

-   -   wherein Δd represents a deviation (mm) in the thickness of the        sample for measurement under load and d1 represents a        thickness (mm) of the sample for measurement before the load is        applied.        Further, compressive stress σ (MPa) was determined according to        the following equation:

σ=F/A

wherein F represents compressive force (N) and A represents a crosssection area (mm²) of the sample for measurement before the load isapplied.

The compressive elasticity modulus E (MPa) was determined in the rangeof the compressive force being from 0.1 to 0.2 N according to thefollowing equation:

E=(σ₂−σ₁)/(ε₂−ε₁)

wherein σ₁ represents compressive force (MPa) measured when thecompressive force is 0.1 N; σ₂ represents compressive force (MPa)measured when the compressive force is 0.2 N; ε₁ represents compressivestrain measured when the compressive stress is σ₁; and ε₂ is compressivestrain measured when the compressive stress is σ₂.

Moreover, the recovery rate from deformation and the maximum compressivedeformation rate were calculated according to the equation below,providing that the thickness of a sample for measurement before load isapplied is d1, the thickness of a sample for measurement at a point thata maximum load of 500 N is applied or the sample for measurement isdestroyed is d2, and the thickness of a sample for measurement after theload has been removed is d3.

Recovery rate from deformation=(d3−d2)/(d1−d2)×100

Maximum compressive deformation rate=(d1−d2)/d1×100

(3) Measurement of Signal Area Ratios Relating to Silicon-ContainingBonding Units Q, T, and D

The measurement was carried out using a “FT-NMR AV400WB” (product name:manufactured by Brucker Biospin KK) as a solid ²⁹Si-NMR device. Themeasurement conditions were as follows: measuring mode—DD/MAS method;probe—CPMAS probe with 4 mm ϕ; magnetic field—9.4 T; resonancefrequency—79 Hz; number of MAS rotation—6 kHZ; and delayed time—150seconds. Sodium 3-trimethylsilylpropionate was used as the standardsample.

The aerogel was finely cut to prepare the sample for measurement; andthis was packed in a rotor made of ZrO₂ and mounted on a probe to carryout the measurement. Also, in the spectrum analysis the Line Broadeningcoefficient was set at 2 Hz, and the signal area ratios relating to thesilicon-containing bonding units Q, T, and D (Q+T:D) were determined.

(4) Measurement of Density and Porosity

With respect to the aerogels, the central diameters, densities, andporosities of holes (or pores) that are continuously communicating in athree-dimensional reticulate fashion were measured by the mercurypenetration method in accordance with DIN66133. Note that thetemperature for measurement was set at room temperature (25° C.) and anAutoPore IV9520 (product name: manufactured by Shimadzu Corporation) wasused as the measuring device.

TABLE 1 Si Material Added Amount Drying Method Type (weight part)Example 1 normal pressure X-22-160AS 40.0 MTMS 60.0 Example 2 normalpressure X-22-160AS 40.0 MTMS 60.0 Example 3 normal pressure X-22-160AS40.0 MTMS 60.0 Example 4 normal pressure X-22-160AS 40.0 MTMS 60.0Example 5 normal pressure X-22-160AS 20.0 MTMS 80.0 Example 6 normalpressure polysiloxane 40.0 compound A MTMS 60.0 Example 7 normalpressure polysiloxane 20.0 compound A MTMS 80.0 Example 8 normalpressure X-22-160AS 20.0 MTMS 60.0 bistrimethoxy- 20.0 silylhexaneExample 9 normal pressure polysiloxane 20.0 compound A MTMS 60.0bistrimethoxy- 20.0 silylhexane Example 10 normal pressure X-22-160AS20.0 polysiloxane 20.0 compound A MTMS 60.0 Example 11 supercriticalX-22-160AS 40.0 MTMS 60.0 Example 12 supercritical polysiloxane 40.0compound A MTMS 60.0 Example 13 normal pressure polysiloxane 40.0compound B MTMS 60.0 Example 14 normal pressure polysiloxane 20.0compound B MTMS 80.0 Comparative normal pressure MTMS 100.0 Example 1Comparative normal pressure MTMS 70.0 Example 2 DMDMS 30.0 Comparativenormal pressure MTMS 60.0 Example 3 DMDMS 40.0 Comparative supercriticalMTMS 100.0 Example 4

TABLE 2 Thermal Compressive Elasticity Recovery Rate Maximum CompressiveConductivity Modulus from Deformation Deformation Rate Q + T:D DensityPorosity [W/m · K] [Mpa] [%] [%] Area Ratio [g/cm³] [%] Example 1 0.0270.20 94.6 87.2 1:0.10 0.19 88.7 Example 2 0.024 0.42 95.0 87.1 1:0.100.18 88.4 Example 3 0.022 0.68 95.5 86.8 1:0.10 0.17 89.0 Example 40.024 0.43 95.1 87.0 1:0.10 0.18 88.8 Example 5 0.017 1.42 93.7 85.21:0.04 0.17 90.6 Example 6 0.019 0.94 95.2 86.0 1:0.09 0.17 90.5 Example7 0.016 1.64 93.2 84.2 1:0.03 0.16 91.2 Example 8 0.019 0.98 95.1 85.91:0.04 0.17 90.6 Example 9 0.018 1.22 94.3 85.5 1:0.04 0.16 90.8 Example10 0.020 0.85 96.2 86.4 1:0.10 0.18 90.1 Example 11 0.022 0.70 95.6 86.61:0.10 0.18 89.4 Example 12 0.019 0.96 95.0 86.0 1:0.10 0.17 89.8Example 13 0.018 0.10 94.2 85.0 1:0.07 0.17 91.5 Example 14 0.015 1.8492.2 83.2 1:0.02 0.16 92.2 Comparative 0.017 7.40 destroyed 17.3 1:0  0.17 91.2 Example 1 Comparative 0.041 1.25 92.5 84.3 1:0.54 0.18 86.8Example 2 Comparative 0.045 0.15 96.2 87.6 1:0.67 0.19 86.4 Example 3Comparative 0.017 7.38 destroyed 15.8 1:0   0.16 92.2 Example 4

Further, FIG. 1 is a diagram showing a chart of measurement obtainedwhen the thermal conductivity of the aerogel of Example 10 was measuredunder atmospheric pressure by using the steady state thermalconductivity measuring device. According to FIG. 1, it is understoodthat the aerogel of Example 10 has a thermal conductivity of 0.020 W/m·Kat 25° C.

Still further, FIG. 2 is a diagram showing a stress-distortion curve ofthe aerogel of Example 1. According to FIG. 2, the compressiveelasticity modulus of the aerogel of Example 1 at 25° C. can becalculated to be 0.20 MPa.

Based on Table 2, it can be grasped that each aerogel of the Exampleshas a thermal conductivity of 0.03 W/m·K or less, a compressiveelasticity modulus of 2 MPa or less, a recovery rate from deformation of90% or more, and a maximum compressive deformation rate of 80% or more,as well as possesses thermal insulation and flexibility. In addition,the aerogels of the Examples were such that the signal area ratiosQ+T:D, which relate silicon-containing bonding units Q, T, and D, werein the range of from 1:0.01 to 1:0.5 in the solid ²⁹Si-NMR spectra asmeasured by using the DD/MAS method.

By contrast, although Comparative Examples 1 and 4 had thermalconductivities of 0.03 W/m·K or less, they had such large compressiveelasticity moduli as to be week against deformation and were easilydestroyed. Further, Comparative Example 2 had a large thermalconductivity. Comparative Example 3 had a large thermal conductivityalthough it had sufficient flexibility.

INDUSTRIAL APPLICABILITY

The aerogel of the present invention has a thermal conductivity of 0.03W/m·K or less and a compressive elasticity modulus of 2 MPa or less at25° C. under atmospheric pressure, as well as possess excellent thermalinsulation and flexibility that are unattainable by the aerogels in theprior art. Considering these advantages, the application can be in theusages as thermal insulating materials in the construction field,automobile field, consumer electronics, semiconductor field, industrialfacilities, and others. Also, the aerogel of the present invention canbe utilized as an additive for paint, cosmetic, anti-blocking agent,catalyst support, and others in addition to the usage as a thermalinsulating material.

1. A sol composition for aerogel formation containing at least oneselected from a polysiloxane compound having a reactive group within amolecule, and a hydrolysis product of the polysiloxane compound.
 2. Thesol composition according to claim 1, wherein the reactive group is ahydroxyalkyl group.
 3. The sol composition according to claim 2, whereinthe number of carbon atoms of the hydroxyalkyl group is 1 to
 6. 4. Thesol composition according to claim 2, wherein the polysiloxane compoundis represented by the following formula (4):

wherein R₉ represents a hydroxyalkyl group, R₁₀ represents an alkylenegroup, R₁₁ and R₁₂ each independently represent an alkyl group or anaryl group, and n represents an integer of 1 to
 50. 5. The solcomposition according to claim 1, wherein the reactive group is analkoxy group.
 6. The sol composition according to claim 5, wherein thenumber of carbon atoms of the alkoxy group is 1 to
 6. 7. The solcomposition according to claim 5, wherein the polysiloxane compound isrepresented by the following formula (5):

wherein R₁₄ represents an alkyl group or an alkoxy group, R₁₅ and R₁₆each independently represent an alkoxy group, R₁₇ and R₁₈ eachindependently represent an alkyl group or an aryl group, and inrepresents an integer of 1 to
 50. 8. The sol composition according toclaim 1, wherein a content of the at least one selected from thepolysiloxane compound having a reactive group, and the hydrolysisproduct of the polysiloxane compound is 5 to 50 parts by mass withrespect to 100 parts by mass in total of the sol composition.
 9. The solcomposition according to claim 1, wherein the sol composition furthercontains at least one selected from a silicon compound having ahydrolyzable functional group within a molecule, and a hydrolysisproduct of the silicon compound.